FIELD OF THE INVENTION
The invention relates to a triggering circuit for a crash sensor-controlled protective system for the occupant of a vehicle, for example an air bag or seat belt retractor configuration, including:
a firing capacitor which is charged before the accident to a capacitor voltage from the electrical system of the vehicle as an energy source for firing a gas generator, that is for firing an explosive charge or for firing a firing cap of an explosive charge; and PA1 at least one crash sensor which detects the occurrence of sensor values that trigger the firing and which controls the firing of the gas generator by discharging the firing capacitor, by means of one or more contacts. PA1 charging the voltage source (battery) of the electrical system of the vehicle with the firing energy stored in the firing capacitors if the electrical system of the vehicle is per se still intact; or PA1 senselessly wasting firing energy if the electrical system of the vehicle already has a short circuit because of the accident. PA1 which correspond to a genuine crash situation and are therefore intended to trigger the firing of the gas generator, and PA1 those which only correspond to an unevenness of the roadway, that is to say, for example, a pot hole or a branch which has been traveled over, which are therefore not yet intended to trigger the firing of the gas generator.
A triggering circuit of that kind is familiar per se to a person skilled in the art of such protective systems, for example from Published International Application WO 91/05680.
The person skilled in the art is also familiar with the fact that a main problem with such systems is the reliability of firing in the case of an accident. The firing capacitor is intended to store the required amount of energy to be able to reliably fire the gas generator even if the electrical system of the vehicle were to be destroyed in the case of an accident.
However, the invention is based on the fact that it must be certain that the firing capacitor has been sufficiently charged before the accident even if the firing capacitor stores an insufficient amount of firing energy, and in particular with an insufficiently high capacitor voltage, because of an undervoltage in the electrical system of the vehicle lasting for a relatively long period of time, for example because only +8 V instead of +12 V have been present for a long time. The gas generators in fact require adequately high firing energy over an adequately short time period. For that purpose, an adequately high firing voltage, as is seen in the 30 V source in FIGS. 1 to 6 of Published International Application WO 91/05680, is also required at the start of firing.
The amplification of the stored firing energy by increasing the capacitance of the capacitor is often not sufficient because the firing voltage of the firing capacitor may not drop below a minimum value either.
It is possible to remedy that problem by means of a voltage transformer in the electrical system of the vehicle, or in the triggering circuit, with the voltage transformer producing as required, for example +20 V or +30 V from the electrical voltage of the vehicle which is, for example, +8 V to 15 V, in order to charge the firing capacitor with the direct voltage being increased in that way. However, that solution requires a considerable outlay for circuitry, and such transformers are often not operationally reliable for an adequately long time either, as measured in comparison with the long service life of the vehicle.